Cylinders of an engine may be activated and deactivated via activating and deactivating intake and exhaust valves that control flow to the cylinders. One condition where cylinders may be deactivated is during and immediately after a driver releases an accelerator pedal and driver demand torque is low. The cylinder's intake valves may be closed as part of the cylinder deactivation process. Intake manifold pressure may rise after closing the intake valves because of the absence of air flow through cylinders and because air may leak past the throttle and into the intake manifold. If the cylinders are reactivated after intake manifold pressure rises, the cylinders may produce more torque than is requested because large amounts of air may be inducted to the engine cylinders. The engine torque may be controlled via retarding spark, but accurately controlling engine torque during intake manifold pump down may be difficult. Alternatively, the cylinder valves may be reactivated allowing air to flow through the engine cylinders until intake manifold pressure is a desired value before resuming combustion in the engine cylinders. However, pumping the intake manifold down in this way may reduce the engine's response to an increase in accelerator pedal position. Further, it may be undesirable to flow air to the engine's exhaust system since it may disturb a balance of oxygen in a catalyst downstream of the engine, thereby increasing tailpipe emissions.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: adjusting an engine volumetric efficiency actuator while engine cylinders are deactivated to a first position to increase engine cylinder volumetric efficiency via a controller in response to engine intake manifold pressure being greater than a threshold at an engine speed and a driver demand torque, and where the engine cylinders are deactivated via holding cylinder poppet valves closed during an entire engine cycle.
By prepositioning engine volumetric efficiency actuators before reactivating engine cylinders, it may be possible to provide the technical result of controlling intake manifold pressure such that the engine may operate with a desired intake manifold pressure in a short amount of time after reactivating engine cylinders. Therefore, the number of cylinder cycles where transient torque control is provided may be reduced. Further, the air inducted into engine cylinders after opening the cylinder's intake valves may participate in combustion so that fresh air is not provided to the catalyst downstream of the engine. Consequently, engine emissions may not be increased during cylinder reactivation.
The present description may provide several advantages. In particular, the approach may improve torque control during cylinder reactivation. Further, the approach may reduce engine emissions by not exposing the engine's catalyst to fresh air. Additionally, the approach may improve engine responsiveness to torque request increases after reactivating engine cylinders.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.